The present invention concerns wires of amorphous metallic alloys and, in particular, methods and apparatus which make it possible to obtain wires of amorphous metallic alloys by rapid cooling in a liquid medium, these alloys having, in particular, a base of iron.
It is known to produce amorphous wires by spraying a jet of molten alloy into a liquid cooling layer, for instance, a layer of water applied by centrifugal force against the inner wall of a rotary drum or against the bottom of a moving belt. Such methods are described, for instance, in U.S. Pat. Nos. 3,845,805 and 4,523,626.
These methods have the following drawbacks:
The projected jet has a tendency to resolve itself into drops, which results either in discontinuity of the jet, leading to the impossibility of having a continuous wire or in the formation of a continuous wire of irregular cross section.
In order to avoid this resolution into drops it is necessary to satisfy the following operating conditions in the case of iron-base alloys:
The distance between the outlet nozzle of the molten metal and the water must be small, less than about 3 mm.
The rate of ejection of liquid metal must be high, equal to at least about 8 meters per second, that is to say, the pressure of the gas used to project the metal through the nozzle must be high, at least equal to 3.5 bars.
Moreover, the temperature difference between the molten metal and the outside environment is very high and, due to the small distance between the nozzle and the water, it is not possible to use parts which make it possible to insulate and reinforce the nozzle and the reservoir containing the molten amorphizable alloy. It is therefore necessary to use only special materials, such as silica, which withstand high heat gradients well but, on the other hand, support pressure poorly, so that the pressure of the gas used to project the metal through the nozzle is less than 5 bars. There results from this, in general, a speed of the ]et which is less than 10 meters per second, which can lead to a lack of regularity of the jet and to a low speed of manufacture of the wire.
The production of the wire therefore requires a very precise compromise between operating characteristics, a compromise which is very difficult to satisfy in industrial manufacture.
Finally, in the event that a rotary drum is used having a layer of water applied against the inner wall of the drum by centrifugal force, then, in view of the small distance which must be provided between the nozzle and the water, the reservoir from which the jet comes must be located within the drum so that, for considerations of space, the capacity of the reservoir cannot be greater than about 500 g of metal and the length of the wire produced is necessarily limited.
The French patents published under Nos. 2,136,976, 2,230,438 and 2,367,563, as well as the article entitled "Production of fine wires from liquid steel" by Massoubre, Pflieger et al., published in the Revue de Metallurgie for March, 1977 described a method of manufacturing steel wires by cooling a jet of molten metal to solidification in a gaseous atmosphere, the jet being stabilized by a superficial oxidation reaction. This process requires a very long length of path in said gaseous atmosphere in order to obtain the solidification, and it is not adapted to the production of wires of amorphous alloys, since the speed of hardening is not sufficient.